This invention relates to roller bearing assemblies, and in particular to a method of protecting a bearing assembly against oil-out conditions and a bearing assembly made in accordance with the method.
Adhesive wear in mechanical components results when parts which move relative to each other come into contact under loads and speeds sufficient to generate micro welding of asperities on the contacting surfaces. When a mechanical system suffers from a catastrophic loss of lubrication, adhesive wear between such parts leads to galling of the parts and the seizure of the system. The catastrophic loss of lubrication in aerospace systems such as rotorcraft gearboxes and turbine engine bearings is referred to as an oil-out condition. An oil-out condition in gearboxes and turbine engines usually precipitates a bearing failure, which renders the system inoperative.
Depending upon operating conditions such as load and speed, the amount of time from oil-out to bearing failure can be a few seconds to many minutes. Roller bearing assemblies in new turbine engine designs must endure intermittent oil-out conditions under full loads and speeds for at least thirty seconds. It is desirable for roller bearing assemblies in rotorcraft gearboxes to continue to operate for more than thirty minutes following an irreversible loss of lubrication.